Aboard an old Staten Island Ferry named Mortimer, maintenance workers Neil and Dominique inadvertently release a mutant mouse, Steamboat Willie, from a sealed chamber below deck, unleashing a monstrous reality that turns their late-night boat ride into a desperate fight for survival in New York City. As the creature's body count rises, a group of survivors, including a bartender with disillusioned dreams of becoming an artist and a ferry employee who takes her aboard, must band together to escape the killer mouse and uncover its sinister past.